we're just across the street from the boston public library next to boylston street where two bombs exploded yesterday at the world's premiere marathon. the f.b.i. appealed to the public came this evening. the agent in charge, richard deslauriers asked the public for leads and photographs and summed up the investigation this way. >> at this time, there are no claims of responsibility. the range of suspects and motives remains wide open. >> pelley: investigators say this was one of the most photographed areas in the country yesterday. but did anyone capture the image of the person or persons who planted the bombs that killed at least three people and wounded more than 170 including spectator leann yawny. >> i'm alive. and being so close to the blast, you know, it could have turned out way worse. >> pelley: she was one of the lucky ones.

27 of the wounded remain in critical condition this evening. among the dead, eight-year-old martin richard of dorchester, massachusetts. and late today another of those killed was identified. 29-year-old krystle campbell of medfordford. we've also learned more about the two bombs planted near the finish line. they were filled with nails and ball bearings designed to maim as many people as possible at an event that drew runners and spectators from all over the world. >> this was a heinous and cowardly act, and given what we now know about what took place, the f.b.i. is investigating it as an act of terrorism. >> pelley: terrorism on patriots' day. a massachusetts holiday that celebrates the opening shots of the american revolution known to many in boston each year as marathon day. and we have just received word that the third person killed was a graduate student at boston

university, the president of the university posted an announcement a short time ago, but he did not identify the student. there were reports yesterday that one or more unexploded bombs were disarmed. but it turns out there were only two bombs. both of them exploded. homeland security correspondent bob orr is in washington following the investigation. >> reporter: law enforcement officials say the bombs contained an explosive similar to black powder. they were laced with bbs, ball bearings and nails. trauma surgeon said many of the injured have multiple shrapnel wounds. >> they are numerous, numerous. there are people who have 10, 20, 30, 40 of them in their body or more. >> reporter: investigators believe the bombs were hidden in black nylon backpacks. and housed inside sealable metal pots called pressure cookers. pressure cooker bombs can help boost the power of relatively

small devices by briefly constraining the blast. and when the cookers do explode, they can add large chunks of metal to the shrapnel spray. the i.e.d.s have been popular with terrorists. al qaeda published a how-to recipe in an on-line magazine. several of the bombs were used in the 2006 attack on trains in mumbai india. in 2004 and 2010, the department of homeland security warned law enforcement that pressure cooker bombs could present a threat in the u.s. in the failed time square attack in may 2010, a pressure cooker was found amid the bomb component in the back of the suspect's s.u.v. but the use of pressure cooker bombs does not necessarily point to an international terror connection. the f.b.i. still can't rule out a domestic cell or lone wolf. and at the moment investigators have no solid leads on who might be responsible. the f.b.i. is studying surveillance videos and photos

hoping to spot the bomber in the crowd. and lead agent rick deslauriers is appealing for the public's help. >> we are asking anyone who may have heard someone speak about the marathon or the date of april 15 in anyway that indicated that he or she may target the event to call us. someone knows who did this. >> reporter: investigators have now recovered pieces of the backpacks and the pressure cookers. we're also told parts of the circuit board. scott, the f.b.i. at this hour does not know how the bombs were triggered. >> pelley: bob, thanks very much. our senior correspondent john miller is in new york tonight. he's a former assistant director of the f.b.i., and, john, thaws of people were at the race. all of them probably had cell phone cameras. how does the f.b.i. sort through all of that? >> well, first, scott they're very aggressive about making sure they get all of it. something very interesting today. at logan airport as people were departing on international and domestic flights, the customs

and border patrol, the agents from immigration and customs enforcement were greeting them on their way out and saying, "before you get 3,000 miles away, do you have an i-phone, do you have a camera? did you take pictures at the marathon? can we download that right now. can we get that digital media from you? they are going to be buried under a mountain of this stuff. what they're going to do is triage it. they're going to look at when it was taken in terms of how close to the explosion in terms of timing and where it was taken. how close to the two places were the bombs were placed. they're going to go through those first. they will widen out in concentric circles and try to look at every piece they get. >> pelley: we just heard special agent deslauriers ask everyone in the country for tips. how do they sift through all of that? is there a danger that they will just be overwhelmed by all the information. >> they're prepared for a mountain of information. they've activated a computer database that will catalogue everyone of those leads and be searchable. they're going to deploy the

digital investigation visualization system which will help link them to any information in other f.b.i. cases. this is something they've been through before. they've gotten better at it. >> pelley: fascinating, john. thanks much very. some of those white tents that you see behind us were medical tents for the marathon. and they turned out to be life-safers. here's elaine quijano. >> is it tough to talk about this. >> reporter: this doctor was a volunteer in the medical tent. he was treating a national guardsman for foot blisters at the time of the explosion. >> people started to run all over the place. got panicky. when he said that's definitely a bomb, we responded. >> reporter: almost everyone in the tent rushed to the wounded. >> that's what changed me. that five minutes i was at the finish line to see the sidewalk that was now blood red, literally everywhere. >> reporter: what did it sound like? >> a lot of orders being given. a lot... not a lot of panic.

nurses, the doctors, they were like they were ready for this. they knew what to do. >> reporter: the battlefield injuries of one man are unforgettable. >> he came in in a wheelchair with a turn cut on his right leg, left leg and his tibia bone, his leg bone there with nothing around it. no skin, no foot, no leg. >> reporter: what goes through a doctor's mind when you witness the carnage that you witnessed? >> at the time i don't think you think about that. i think you just try to help the people. it's like police and fire and the physicians, you just try to help people who need help. >> reporter: but what sticks most in his mind is this woman he treated and the last thing she asked him before she left. >> what's your name? and you tell them your name and you get choked up because they're telling you, they're giving your name. now you're... they want to thank you. they thank you and it's like, no, this is real. >> reporter: scott, it's estimated about half of those

most severely injured survived because dozens of doctors and nurses were already on hand and were able to quickly triage the wounded. >> pelley: thanks, elaine. we're joined now by deval patrick, the governor of massachusetts. governor, the f.b.i. does not seem to have much in the way of leads. i wonder if they have given you any reason to believe that there is an ongoing threat. >> not that there's an ongoing threat, no. there's a very, very broad and deep and i think methodical investigation going on now at the blast site or the blast sites. and as you know, scott, and they've talked about publicly, they are literally going through square inch by square inch along a several-block area gathering and cataloguing evidence and putting together a scene and ultimately a case. and i think i'm confident that with time -- and we'll have to

give them the space and have the patience to let them do their job -- but with time there will be an arrest and we'll bring someone to justice or someones. >> pelley: governor, do you have any concerns about the way security was handled at the marathon yesterday, about how these bombs got planted? >> well, i have concerns because this happened. i think everybody does. but, remember, we've had 116 years of incident-free marathons. and every single year we've learned lessons from the marathon before. i am so, so regretful that this lesson is a tragic and bloody one. but we'll learn from this as well. and the marathon i think next year will probably be bigger and better than ever. >> pelley: governor deval patrick, thank you for being with us. 76 patients remain in the hospital this evening. 17 of them are in critical condition. in some ways the injured were lucky because medical teams were

already at the finish line to help the runners. and some of the best hospitals in the world were nearby. we visited one of them, brigham and women's hospital, a little bitterlyier today. brigham and women's is five minutes by ambulance from the scene of the attack. among those in the emergency department were trauma surgeon joaquin havens, dr. ron walls, the chairman of emergency medicine and trauma surgeon dr. zara cooer. >> there were two things going through my head. one was actual fear. myself just because i hadn't been in such a situation like this before and i really did feel like it was a war zone in some ways. and then another feeling was reassurance because i think that everybody really pulled together in a very remarkable way. >> pelley: the patients that you treated, what did you see? >> significant amount of burns second- and third-degree burns as well as penetrating trauma from shrapnel to the face, to the neck and to the upper

extremities. there were traumatic amputations from the blast. very, very sick patients that needed help. >> there were three patients in total, i think, who had obviously planted the shrapnel that was part of the device. so small two- to three-millimetre ball bearing type or bb-type pellet objects and small carpenter nails about half a centimeter long. >> pelley: nails and ball bearings, bbs that you believe were part of the bomb itself. >> they wouldn't be out there anywhere unless they were part of the device. >> pelley: there have been a lot of advances in acute trauma care on the battlefield over these last ten years. did any of that come into play in the emergency department yesterday? >> absolutely. in fact, the conflicts in iraq and afghanistan have taught us an incredible amount about how to manage wounds like this. >> pelley: that you patients that you received, a lot of them had had first aid right there at the finish line of the race.

did that save some of the people? >> absolutely. we had patients arrive with turncuts in place which most certainly would have saved their lives from bleeding to death. >> pelley: without the turncuts some of these patients could have bled to death before they ever reached the emergency department. >> absolutely. pelley: is there anything else in your experience that compares to this. >> the last time i saw the hospital anywhere near this was 9/11. we were told to prepare the hospital for an influx of burn patients. and then we all waited for many hours and nobody came. this time we were able to help a lot more people. and that was great. >> pelley: eight children were taken to boston children's hospital. dr. jon lapook has been talking to the people there. jon, what did you find out? >> scott at boston children's hospital which is where most of the kids were taken, three kids remain. there's the nine-year-old girl and a 10-year-old boy who had that very severe leg injuries. they were operated on yesterday. they remain in critical condition with breathing tubes. the one piece of very good news

is that the two-year-old boy we talked about yesterday who had the head injury he was in the intensive care unit, he's doing very, very well. he's talking. he's playing. one of the doctors told me he's covered by so many play toys and stuffed animals that you can barely see him and what may be the best medical sign of all he's eating chocolate chip pancakes. >> pelley: good news. thank you, jon. one child did not survive yesterday. he is martin richard. we'll have his story in a moment. and the role fate played in the tragedy. when the cbs evening news continues from boston.

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now i'm a believer. you'll be a believer, too. learn where to find your number at drscholls.com. >> pelley: back now from boston. for the spectators at the marathon, whether they lived or died, were injured or unharmed, it was at least in part a matter of luck and where they were standing. don dahler has a survivor story. >> a couple blocks over. reporter: long-distance running is a shared passion for david comestock and susie eisenberg-argo. the couple is from texas. >> when you cross that finish line you're not crossing 26.2 miles. you're crossing probably, you know, 3,000 miles of training leading up to that event. >> reporter: this was his sixth boston marathon and her 10th. >> we agreed that she would run on the right side when she finished so that in the crowds i could pick her out and she could pick me out. >> and about 100 yards to finish, the bomb goes off.

>> reporter: that's her highlighted here running just as they had planned. you can see her in this photograph at the moment of the second explosion. >> i looked. i see the smoke coming out of the building. my immediate reaction was just shock. >> reporter: what does a bomb feel like? >> it was an explosion. i felt just debris just hit me but i didn't know what... i still... >> reporter: did you feel the force? >> i did. i did. you still don't... it was so quick. i didn't know what had happened. >> i was extremely worried. i didn't know where she was. i knew she was expected to finish at the time right when the blast occurred. >> and i kept going until i heard dave screaming my name. >> she came through with a moment of elation. >> the moment we saw each other we just embraced. >> reporter: have you thought about what might have happened if you had been on the other side of the road. >> why we chose to go on the right side, it mass meant to be. >> reporter: they say they'll run in next year's boston marathon to prove that whoever did this that life isn't defined

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and now an eight-year-old child has become the symbol of the tragedy here in boston. his name was martin. and jeff glor has his story. >> this picture of martin richard was taken after a school project last april. today it is heart breaking. in dorchester friends left flowers and a soccer ball formatter inwho played on the local team. hoe hey called enron's kids were teammates. >> a smile for everybody's face, whether he won or lost he was always one of the brightest on our team. >> reporter: family friends told us the richards were nearly always together. like yesterday at the finish line of the race. they often ran together as a family. martin's mother and younger sister were also injured in the blast. his father, bill, released a statement asking for patience and privacy. "my dear son martin has died from injuries sustained in the attack on boston. my wife and daughter both recovering from serious injuries. we thank our family and friends for their thoughts and prayers. tonight so many in this city are

thinking about a father and a family who lost a son, and a neighborhood that lost one of its brightest lights. scott, martin's mother suffered a serious head injury. his seven-year-old sister lost one of her legs. >> pelley: jeff, thank you very much. one of the heroes at the finish line, the man in the cow boy hat, has experienced tragedy before. his story just ahead. anyone have occasional constipation, diarrhea, gas, bloating? yes! one phillips' colon health probiotic cap each day helps defend against these digestive issues with three strains of good bacteria. live the regular life. phillips'.

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>> pelley: one of the striking scenes from the terror attack here in boston came just after the explosions. the smoke hadn't cleared before some by-standers were jumping over the barricades to help strangers. one of those good samaritans has quite a story himself. and here's terrell brown. >> reporter: this photo is one of the first captured shortly after the blasts went off. the man in the cow boy hat is 52-year-old carlos arrendondo who ran toward the chaos when others were running away. >> blood is everywhere. people asking for help. people crying. and people running away. the smoke and the smell, too, was very powerful there. >> reporter: america has heard arrendondo's story before when

his 20-year-old son was killed in iraq in 2004 he was inconsolable. in agony and rage he set a van on fire and received help through counseling. search years later his other son committed suicide. arrendondo was at the marathon as part of a healing process giving out flags at the finish line in honor of veterans. when the bomb went off he ran to the aid of a man lying on the sidewalk missing his legs. >> i went to the ground to comfort him. he's okay. the ambulance is on the way. stay still. don't move. i ended up picking him up from the ground to put him in a wheelchair. they just arrived. >> reporter: you see yourself as a hero? >> no, i'm not. reporter: why? because i wasn't doing nothing different from the others first responders who were right at the scene. >> reporter: arrendondo said he could not help his own sons but he believes fate helped him to save someone else's son

yesterday. what would they have thought of what you did yesterday? >> they will see a father who really cares for others and also who loved them and never going to forget them. >> reporter: as he left the scene yesterday arrendondo had one flag left. he told those around him, america is bleeding. terrell brown, cbs news, boston. >> pelley: the spirit of boston. that's the cbs evening news for tonight. for all of us at cbs news all around the world, i'm scott pelley in boston. good night. captioning sponsored by cbs captioned by media access group at wgbh access.wgbh.org we're here! we're going to the park! [ gina ] oh hey, dan! i really like your new jetta! and you want to buy one like mine because it's so safe, right? yeah... yeah... i know what you've heard -- iihs top safety pick for $159 a month -- but, i wish it was more dangerous,

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the boston marathon bombing the day after. >> something just blew up? >> boston made of mark wahlberg's heart break. hollywood extending support. >> all you guys out there on the east coast, what a tragedy. >> terrifying new images that people who risked their lives to save the in